[Draft] PoC for block-consistent balance fetching

[ashleychandy]

Description

Opening this as a draft PR to validate an issue around balance fetching consistency when processing auction data. This implementation should be considered a proof of concept (PoC) to gather feedback on the proposed approach before refining it into smaller reviewable changes.

Changes

• Add support for block-pinned balance fetching.
• Make solvable order balance filtering use the auction block instead of the latest block.
• Update balance reads and simulations to execute against a specified block.
• Introduce request deduplication for concurrent balance fetches.
• Refactor balance cache handling to support block-aware fetching.